Many new communications devices and related services have emerged, to allow people to communicate freely as they roam, without the need for a fixed network connection. In particular, modern digital public wireless telephone networks offer customers a wide range of voice and data communication services combined with a high degree of mobility. In this context, situations arise in which it is desirable to obtain information about the physical or geographic location of a mobile communication terminal and/or its user. For example, some carriers offer services in which the user at the mobile station may request location information and/or information about the surrounding geographic locale, for display on or audio presentation from the mobile station. As another example, some carriers and/or other providers offer location services that allow an authenticated third party to request and obtain the location of a mobile station, for example, so that a parent can obtain information about the location of a child or other relative.
Wireless carriers use various location determination methods today. Many of the current techniques require prior knowledge of locations of wireless network equipment that may be sending and/or receiving transmissions over the air to/from a mobile station seeking a position determination. A knowledge base or database of cell site and/or sector information is sometimes referred to as a base station almanac or “BSA.” Some location determination methods (e.g., Advanced Forward Link Trilateration) require accurate and complete Base Station Almanac (BSA) information. A carrier providing a position determination service or other services based on mobile station location will often maintain a highly accurate BSA with regard to the carrier's own base stations, e.g. to support AFLT position determinations for mobile stations that use its facilities.
However, the carrier's customers roam, and at times request position determination or location based services while their mobile station's are receiving communication service through another carrier's facilities, that is to say through one or more base stations that may not be identified in the BSA data. BSA data for facilities or networks that are visited by the carrier's roaming customers may not be so readily available or accurate. Some of the other operators may be ‘partners,’ with whom the home service provider has some favorable arrangements, but at times, the subscribers will receive service from networks of other carriers with whom the carrier does not have any close ties. The home carrier will have different agreements with the various other parties, and the different agreements will provide different levels of data availability with regard to the other network facilities that may provide service to the home carrier's roaming customers. BSA information changes constantly as operators modify and upgrade their facilities. Also, base station data, such as might be needed in a BSA, includes highly proprietary information. Some carrier's do not have the capability of providing relevant information, and others refuse to share the proprietary BSA information for their base stations, particularly with parties that they consider competitors rather than partners.
The industry is moving toward mobile station position determination based on Global Positioning System (GPS) measurements taken by the subscriber's GPS enabled mobile station. To support such services, a network architecture has been developed that includes a position determining entity (PDE), which communicates with a mobile station (MS) having a global positioning satellite (GPS) receiver to determine the location of the MS. For private user plan applications, such as providing location for the MS user or to an authorized third party, the communications between the PDE and the MS utilize an available data link through the network. Mobile devices roam freely, although they are typically associated or ‘homed’ on a network of the carrier or service provider with which the user subscribes in their normal home area or region. For the private user type location applications, the PDE typically is an entity operated by the home provider. To optimize performance, the mobile wireless networks typically offer satellite acquisition assistance to the mobile stations; and that assistance also relies on BSA information, as discussed below.
A GPS position determination requires a receiver to take measurements from signals received from a number (typically three or four) of the satellites of the GPS system. The array or constellation of GPS satellites transmit highly accurate, time coded information, which a GPS receiver processes in order to determine its three-dimensional location on the Earth. The constellation of GPS satellites provide coverage over the entire surface of the Earth. However, over any given point on the globe, only a smaller subset of the constellation of GPS satellites will provide receivable transmissions or be ‘in view’ in the particular area.
To perform location computations requires certain data about the transmitting GPS satellites. Ephemeris data or “ephemeredes” specifies the precise orbit of each satellite and can be used to calculate the current location of each satellite. The satellites transmit the ephemeris data for use by GPS receivers, and a ground control station periodically updates the ephemeris data to maintain accuracy. Almanac data is a subset of ephemeris data. Each GPS satellite broadcasts the almanac data for all the GPS satellites in the GPS constellation. A GPS receiver can capture the almanac data and/or the ephemeris data by locking onto the signal from one satellite. However, the transmission time for the data is relatively long. When a receiver must wait while it captures this data, the time to first position computation (first fix) may be several minutes or more, which is typically unacceptable for mobile station applications.
To address this data issue, the mobile communication industries have developed Acquisition Assistance (AA). With this approach, the PDE or another node of the wireless communication network provides a satellite almanac data to the mobile station. However, to optimize performance, the almanac data is tailored to the area in which the mobile station is operating. Rather than sending the almanac data for the entire GPS constellation of satellites, a subset of almanac data is provided for those satellites currently in view from the expected location of the mobile station.
The PDE or another node of the wireless communication network that provides the Acquisition Assistance (AA) selects the subset of GPS satellite ephemeris data and/or almanac data for a particular mobile station based on a preliminary fix of the mobile station's location. However, in many current deployments, the preliminary fix (pre-fix) uses the data from a BSA database. Essentially, the wireless network uses its resources to allow a pre-fix determination based on network information from the BSA. Then the PDE or another node compiles the appropriate acquisition assistance data and sends it to the requesting mobile station, for use in taking measurements of the appropriate satellite signals. Hence, even the GPS position determination is dependent on the availability and accuracy of serving base station information in the service provider's BSA database. As with other location techniques requiring BSA data, it is a challenge to provide location information for a mobile station roaming outside of a carrier's coverage areas.
The industry introduced a possible solution, Location-Based Service V2 Roaming. This version included roaming capability based on a carrier deploying both a Mobile Position Center (MPC) and a Position Determine Entity (PDE). However, it has been very challenging for operators to comply with this complex roaming solution. Thus, a simpler, more efficient process is needed.